#!/usr/bin/perl -w

use strict;
use File::Basename;

my $plProgName = basename($0);
my $plBaseName = fileparse($plProgName,'\.[^\.]*');
my $input      = $ARGV[0] || &usage;
my $fail       = 0;

if ( $input =~ /[a-z]/i ) {
    &usage(2);
}

print "Big numbers will take a little while...\n\n"
    if ( $input > 100000 );

for ( 1 .. $input ) {
    my $up         = $_;
    my $last_digit = substr($up,length($up) - 1,1);
    my $mod = $input % $up;

    next if ( $last_digit == 5 or $last_digit = 0 );

    if ( $mod == 0 ) {
        $fail++;

#        print "\$fail: $fail\n";

        unless ( $input == 1 or $input == 2 or $input == 5 ) {
            if ( $input == $up and $fail == 2 ) {
                print "$input is a prime\n";
                exit(0);
            }
        } else {
            print "$input is a prime\n";
            exit(0);
        }
    }
}

print "$input is \c[[1mnot\c[[m prime.\n";

sub usage {
    my $errcode = shift || 1;

    print "\nUsage: $plProgName integer\n\n";
    exit($errcode);
}